Mercenary

A mercenary is generally a soldier who fights for money (although some fought for perferment).

In period they were used to supplement (or substitute for) a kingdom's army :: their main drawback lay in the fact that, once the principle of fighting for money had been established, it was not long before the concept came along of changing sides in return for more money.

At one stage medieval Europe was studden with mercenary companies, led by the like of Sir John Hawkwood, who had elevated their art from fighting for money (and spoil) to not despoiling a territory if they were given enough money to go elsewhere (qv Danegeld)